Flexible insulated duct



Nov. 9, i965 CQA, scHRoEDER ETAL 3,2%,459

FLEXIBLE INSULATED Duc'r Filed Feb. B, `1963 4 Sheets-Sheet 1 l *fA /00 /0:-- /05 INVENTORS Nov. 9, 1965 c. A. scHRoEDER ETAL 3,215,459

v FLEXIBLP: INSULATED DUCT 4 Sheets-Sheet 2 Filed Fab. 8, 1963 lN0 y9 1965 c. A. scHRoEDER ETAL y 3,216,459

,FLEXIBLE INSULATED DUCT 4 Sheets-Sheet 3 yFiled Feb. e, 196s INVENTORS O/VEVS llfI//r t@ It .4,

ma.. fz. 06/- Nov. 9g, i965 v c. A. scHRoEDER ETAL 3,26459 I FLEXIBLE INSULATED DUCT 'Filed Feb. a, 196s I 4 sheets-sheet 4 gxggmmvm Trae/V56 Patented Nov. 9, 1h65 3,216,459 l FLEXIBLE INSULATED DUCT Clifford A.' Schroeder, Los Alamitos, and Quentin L. Clark, Sherman Oaks, Calif., assgnors to Pittsburgh -the ducts due to the porous and fibrous nature of the ini sulation material.l

Since air-conditioning `and heating'system ducting must i extend throughout a building and is positioned in attics,

walls, and between floors of multi-story buildings, the):v ducting often passes through extremely restricted 'spaces Plate Glass Company, Pittsburgh, Pa., a corporation of 5 and around numerous corners and bends. Thus, for in- Pennsylvya stallation purposes, it is often desirable to have a flexible l Filed Febl?, 1963., Sel- N0- 257,196 duct which can be readily passed through restricted spaces i iii Ciaiiiis' (Ci issf'iw) and around comers without requiring modification of the Thi ti. t. l. f d structure of the building or special construction. Als atiioii iiiii iiiiliiinmiliii ipp icaiioii ii our Pen 10 though short lengths of flexible ducts are often used to iig appticatioii liiie sa sii iiiise Piicxiqaiid iifieliiziofi iid pass through these restricted spaces and around corners;v Appiziislgig a iig me mi o i8 o ed it is common practice to limit the use of this flexible ductpri ing to these particular locations. This limited use oty This invention relatesto insulated ducts for conducting flexible ducting is a result of the higher cost per Hmm.'v itiir oi iiieitgiSei-iiis ii'iiiiii iiiii. iii paiiiciiiai. this iiiveii` 15 foot of llexible ducting as compared to rigid ducting andv ioii is ii. e .i0 ii ci o. iiiis type Wiiicii is compiira due to the poor air-ow characteristics of conventional iiveiy iieiiiiiie iiiid iiiiiiipiiisiiie ii. 'vcisaiiie and Piafiiiciii exible ducting. The air-ow characteristics of a duct are use. While this application is directed to the duct itself, extremely imponam in that if a panicular type of duct aii'appaiimis and iiieiiioii 'for miiiiiiig iiie diici is described resists the how of air` therethrough to an objectionable fo-i ii moi-.e iiioioiigii iiii-iieisiaiiding of i-iiejstmciiiie and 2O degree, the size of the duct must be increased or the cogililgur-atwn 0f the duc'i d i capacity of the vair-circulating blower must be increased sie are iiiiiiieioiis, eieiii types of iicis and coiiin order to pass a sufficient amount of air through thaty diiiis for tiaiiisiiiiiiiiig .air and other gases imm (.iii piace duct to accomplish the heating or air-conditioning. The ii.) another .The piiiiiciiiiii pui-pole foriiiiiiiiiiiiiiiig iiie resistance to air-flow through a duct is commonly referred iiii or gas and iiie iype 0i gas being iiiiiisiiiiiied gieiiiiy 25 to as the static friction of the duct which is measured" iiifiiieiis.iiie physicai ieqiiiieiiieiiis wiiicii .ai-ii desiiiid by standard tests wherein air is passed through a predefor a. iiiiiiiciiiiii" coiidiiii or duct' -iii iii@ iieiiiiiig and aii' termined length of duct and the pressure drop through the conditioning of vaiiiiiis iiyiies of biiiiiiiiigs ii .has becoiiie duct is observed. Most conventional liexible ducts are ieiaiiviyiomiiioii in provide a iiiiiii iiiiiiiiiig and air' fabric, or other impervious material, reinforced with wire conditioning iysieiii iii siicii a Sysieiii aii'.is iieiiied 0i '30 and therefore have an irregular or icorrugated inner wall cooied iis. desired and ciiciiiiiied iiiioiigii viiiiioiis diicis i0. that is impervious.' Further, such irregularity of the inner iiie iiidiviiiiiaimoms for. discharging iiie heated 0i .ciioieii wall of the duct is increased by bending the duct aroundiii iiiio iiie iiifiiii' The di'iciii are geiieiaiiy posiiioiied a comer and thus these ducts have a relatively high static Wiiiiiii' iii@ viiiiigswiiiis aiiics 0i be-iweeii fiom-S 0i friction characteristics. Also, the impervious inner surmiiiiiiiie iiooi biiiiiiiiigs l v face of such ducts provides very little acoustical insulaii is giiiiiiiaiiy iieesiaiy 0i iii eiisi desiiiibi io iii' tion. Thus, conventional exible ducting is used sparingly Siiiiiie die. aii'coiidiiioiiiiig and iieaiiiig diicis for Piiipei in air conditioning Iand heating systems to avoid lthese uniiiid eiiiic-iiiiopeiaiioii of iiie sysiiiiiif For iiiiaiiiiiie desirable characteristics of conventional flexible ducting.

iii .a iypicai iesiiiiiii 0i'. .Oiiiei Siiigie'ievifi biiiiiiiiig Accordingly, it is a principal object of this invention to v iiaviiig ii ceiiiiiii iiii'coiiiiiiiiiiiiiig .iiiiii healing. syiieiii 40' provide a novel form of insulated duct which is highly iii@ iiiicis are Comiiioiiiyposiiioiied iii-iiie attic wiiii iiiiii' exible and yet highly resistant to collapsing from cxvidual branch ducts leading to each room of the building. temany applied radialforces or exing Iii iii-ie Siiiiiiiieiiiiioiiiiis iiviieii. iiie Sysieiii is being Sed io Another object of this invention is to provide a exible i 90 iii? biiiiiiiiig iiie air' Wiiiiiii iiie iiiic iiiciiesieia' insulated duct which is relatively inexpensive to manutively high temperatures and yet the air passing through facture and lends itself to easy installation iiie iiiicis is i'eiiiiiveiy cooi foi ciioiiiig iiie rooms' Thus A further object of this invention is to provide a novel 1 it has become common practice to .use insulated ducts so form of insulated duct wherein the insulation is ex iiiiii iiie iieai iiiiiisiei beiweeii .the .iiiieiii of ihe d i'ici iiiiii posed to the interior of the duct for producing acoustical the exterior of the duct, Le., warming of the coolair being insulation as wen as thermal insulation circulated, is minimized to increase the overall eiciency v A stm further obj-ect of this inveon is to Provide and effectiveness of the system. Likewise, in the winter a exible ins-lated duct wherein the infernal surface moiiiiis Wiieii warm iiii is cii'ciiiiiieii iiiioiiiiii iiie diicis i0 of the duct is relatively smooth to produce good air-flow iieiii iiie moi-iis iiie temperature iii the attic may be? ieiii' characteristics through the duct. A more specic object tively low, so that the heat loss from the duct to the attic is to produce Such a duct wherein bending of the duct would be excessive if the ducts were not insulated. 55 around a Comer does not appreciamy affect the Smomh ii is ifiiiiiiiiieiy. coiiiiiiiiii piacii iii present coiiiiiieiciai interior surface and, thus, the good air-flow character- -A' and residential installations to use sheet-metal d ucts for sucs- Of the duct aref maintained in the bent condition. conducting the heated or cooled air to the various rooms. Another Object of this invention is to. provide a novel These .Sheeiiiieiiii diicis aie iisiiiiiiy. iiisiiiiiieci Wiiii, fiber form of insulated duct wherein the insulation is exposed giass iiiiiiiiiiiioii biiiiiiieiii iow density iiiiiii Wooi etc" to the interior of the duct for sound insulation and yet iiiai aieeiiiiei Wrapped around iiie eiiieiioi of the Siieei` mechanically supported from the interior of the duct to metal duct or are secured to the interior of the duct. ln maintain a Smooth md reguhr interior Surface many commercial buildings, it is necessary to secure the A further ob'ect ci this invention is to provideia rovel insulation to the interior of the duct in order to provide f f bll l t d d t h f th acoustical insulation, so that sounds from one room are Omi o exi e iiisii a e iic W eieiii Wire dorms e not transmitted through the duct to another room. Posi-y siriiciiiiai Supioii for the msu ating maieriai an prei/eins tioning the insulation on the interior of the duct also serves riidiai coiiiipsmg oithe duct b t s uch Wire dqes not m' to reduce the noise level caused by the movement of air hlbl bendlng, exlng 0f longitudinal COHaPSmg C'f the through the duct from the central system. Mountingthe dUC- insulation on the interior of the ducts acoustically insulates other and mOrC dtalled Objects and advantages of this invention will appear from the following descrip tion and the accompanying drawings.

aziaiss l rplet'ed duct with the plane of the section taken perpen- `tiicular tofthe axis of the duct. FIGURE 4 is an enlarged longitudinal fragmentary sectional view. zof the duct taken substantially on the line 11--11 as-shown in FIGURE 10.

FIGURE is 'a sectional view of the duct of this inlvention taken substantially on the axis of the duct and illustratingl the duct as beiug exed to bend around a 90 corner.

FIGURE 6 is a fragmentary sectional view of'a modi- !ied formof the duct of-this invention.

FIGURE 7 is an elevation view of our duct being m- 'stalled between two sheet metal conduits. with portions FIGURE 8 isa fragmentary sectional view of a second modified form of the duct of this invention.

il FIGURE 9 is a fragmentary sectional view ofv a third modified form ofthe duct of this invention, and of the collapsingmandrel usedv in manufacturing such form.

l l' FIGURE 10 ,isv a .cross-sectional view of the modilied 1 form .of'the duct shown in FIGURE 16.

FIGURE 1l is a cross-sectional view similar toFIG- vURI-E'17, showing the modified form of duct shown in FIGURES 1 6 and 17 in its non-strained lcondition as it would appear after removal from the collapsing mandrel. lFIGURES 12, 13, 14, 15 and lillustrate the successive steps, in that order, for providing an end closure on the duct of this invention.

FIGURE 3 is a fragmentary sectional view of a comaereas@ has been found satisfactory to use a spacing of about V2 inch between wire convolutions in a duct having an `internal diameter of six inches. If a structurally stronger or weaker duct is desired, the spacing maybe decreased of the mandrel assembly 24.

or increased, respectively, by'adjusting 4the rate of movement of wire feeding assembly 61 relative to the rotation When the mandrels 29 and 30 are covered with the desired length of duct (usually the length of rthe mandrels), the wire is severed between the mandrels and adhesive applicator ,68 and the end is releasably secured to the mandrels by any convenient means such as a clamp (not shown).

Referring now to FIGURE 1, the mandrel assembly 24 is schematically shown yas pulling the wire 72 olf the wire feeding assembly 61 yand through the adhesiveapplicator 68. An overhead support apparatus, 'generally designated 79, may be provided above the machine 10 for4 supporting the sheet-like member o'r blanket 80 of insulation material which is used in the duct. The sheet- `i114 cross-sectionforillustrating the flexibility of the duct.

FIGURE 15A is an enlarged fragmentary sectional l view of the end closure for the duct in its intermediate stage o f construction as illustrated kinFIGURE 15.

FIGURE 17'illustrat`es themanner of connecting two ducts of this type to one another.

The iiexible insulated' duct of this invention may be ,constructed on an apparatus of type `described in our aforementioned application of which .this is a continuadesired inside diameter 'of the duct.' Cylindrical mandrel assembly 24 is comprisedof a pair ofv semi-.cylindrical mandrels 29 and- 30 that are adapted to collapse radially't-owardeach other to facilitate the removal of a completed'duct from the assembly. lfhe manufacturing apparatus 'includes means for supporting a wire feeding assembly, `generally designated 61, and an adhesivev applicator assembly, generally designated 68, and moving i them longitudinally along the mandrel assembly 24 in synchronization with the rotation of the mandrel assembly for feeding adhesive-coated wire 72 onto the mandrel assemblyv in a continuous helix as shown in the lefth'and portion of FIGURE 2. A mold release compound may be applied to mandrelassembly 24 first to inhibit adhering of the wire72 thereto.v The spacing between each convolution ofwi're 72 is established 'by the predetermined adjustment of the rate of longitudinal movement of thewire feeding assembly 61 relative to the rate of rotation of the mandrel 'assembly 24. Although this spacing between convolutions of wire may be greatly -mandrels like member or blanket has a width equal to the length of the duct which is being produced (generally the length of the mandrels 29 and 30, although the duct produced may be shorter).v Although it is not essential,

with some types of insulation blanket we prefer to apply a thin coat of glue, adhesive or other type of coating to the portion ofthe surface of the blanket 80 which 'is to be applied to the mandrels 29 and 30. This coating may allel to the axis of the mandrel assembly 24. The mandrel assembly 24is then rotated towrap the blanket 80 around the mandrels 29and 30. A pressure pan $3 or series of rollers (not shown) may be provided and extend the length of the `mandrels for engaging the outer surface of the blanket to hold the blanket uniformly o n the mandrelsand apply suflicient pressure to cause the vblanket to adhere to the adhesive-coated wire. The pressure pan 83s may be moved out of engagement with l the blanket for subsequent operations. After the blanketl 80'l has been' partially wrapped onto the mandrels 29 and 30,'

the other end 84 of the blanket is released from the support apparatus 79and the entire blanket is Wrapped around the mandrels to form an encircling tubular mem- 'ber or blanket of the' insulation material. Although as many' wraps of vinsulation blanket 80 may be made as is desired or required for the particular duct, FIGURE l (and FIGURES '2 and 3) shows a suficient length of blanket to make two wraps around the The number of wraps of insulation blanket Whichare usedwill obviously depend on the insulation quality ofthe blanket and the desired insulation properties of the completed duct. We prefer touse an insula- 'tion blanket which is compressible and yet has some resistance to lengthwise and width-wise stretching of the blanket, such as, but not limited to: ber glass insulation blankets of a typical density of 0.3 to 1.0 pound per cubic foot, low-density rock wool, exible plastic foam insulation, o r rotary liber glass insulation blanket. Further, when a fibrous type of insulation blanket is used that has a particular predetermined orientation of the individual fibers where the fibers tend to extend more in one lengthwise direction of the blanket than the other, we prefer to orient 4the blanket when applied to the glued wire on the mandrels 29 and 30 such thatl the fibers extend circumferentially around theimandrels rather than longitudinally along the length of the mandrels. Forexample,

it is inherent in the process for vmaking glass fiber prevent collapse of the duct in a radial direction upon the application of moderate forces that may be encountered. But also, since tlexibility of the duct is of parathe length of the mandrels 29 and 30. Although the l reasons for this particular orientation of a fibrous insulation blanket will hereinafter become more apparent, at this point it should be 'noted that this liber orientation tends to prevent circumferential expansion, i.e., enlarging'of tbe duct,'and permits longitudinal collapsing ofthe duct, such as by flexing, without tending to compress the bers length-wise which could cause undesirable .bulging ofthe fibers.

Means are then applied 'to the insulation blanket 80 for keeping it wrapped to the mandrel for subsequent operations, and these means may be of various types such as means for securing the outer end 84 to the previous convolution of blanket or encircling the blanket. For example, it has been found satisfactory to vuse staples along end 84 which pass into the previous convolution of blanket. Also, it has been -found satisfactory to use a tie cord 85', such as conventional fiber glass tie cord, 'which is wrapped around the outside of the insulation blanket 80 in a 'continuous helix and slightly compresses the blanket 80. .The convolutions of the tie cord 85 are substantially spaced one from another as shown in FlG- URE 2, the actual spacing depending onsuch factors as the size of the duct and the wall thickness of the `insulation. A exible and substantially nonexpansible sleeve 86 of a length equal to the length ofthe duct which is being produced'is then positioned-on the shaft 25 at the end of mandrei'assembly`24. The' sleeve 86 may be of any conventional material, but it is more desirable 'if the materialis relatively Jflexible, relatively unaffected by the temperature changes to which the duct is to be subjected, and suiciently inexpensive to be rused without greatly increasing the overall cost of the duct.

lVarious types of thin Vinyl plastic sleeves have been found to be satisfactory. l l

A pairof hoops 87 and 88 may be usedto facilitate the installation of the sleeve 86 over the exterior of the insulation blanket 80. The smaller hoop S7 is inserted inside of the sleeve 86 and the larger hoop 8S is fitted over the exterior of Ithe sleeve, thereby clamping the sleeve lbetween the hoops as shown in FIGURE 2. The

sleeve 86 is then pulled over the exterior of the insulation blanket 80 and is preferably of a size t-o slightly compress the insulation blanket 80. The hoops 87 and 88 may then be removed and the ends of the wire 72 unclamped from mand-reis 29 and 30. The mandrels 29 and30 are then collapsed toward each other, as previously described, and the completed duct may be slid off the mandrels.

The insulated duct of our invention is completed by the installation of the sleeve 86 and it will be noted that 'no heat curing is necessary in producing our exible insulatedduct. Connectors of any convenient type may be added to either or both ends of the duct as desired for facilitating. ,1 on-the-job installation, and means vsuch as a vinyl sleeve, may be added on either end for preventing fraying of the insulation blanket. The outer surfaces of the mandrels 29 and Sil then may be cleaned with an appropriate solvent to remove the excess glue and mold release compound, and new coating of mold release compound may be applied for producing another duct in the same manner as heretofore described.

In our nished duct, the insulation member or blanket S is exposed to the interior of the duct thereby producing the desired acoustical insulation as well as providing a. thermally insulated duct. The wire 72 may be of any convenient size, cross-section and material within certain limits and yet exhibit all of the desired characteristics. The wire 72 must have sufficient strength and rigidity to mount importance and yet the wire is formed in a conntinuous helix, the wire cannot be of such a strength as to resist bending of the duct. Further, the wi-re must be suiciently resilient as to notbe permanently deformed upon flexing of the duct. The term Wire therefore as used through this application, including the claims, is intended'to mean and include any element in the form of a slender rod whether comprised of metal,plastic, resincoated fiber or other material andl whether circular or non-'circular in cross-section, if that element exhibits these characteristics of relative tiexibility, resiliency and strength.

For example, we have found spring steel wire to be excellent and by using certain different diameters of wire for the range of different diameters of the ductsthe proper balance between maintenance of radial strength against collapse and maximum longitudinal flexibility has been obtained. Spring steel wire of 0.037 diameter is excellent for ducts of less than 7" inside diameter and spring steelwire of 0.0511" diameter has been found satisfactory for ducts of inside diameters of substantially 7" i up through 16 inside diameter, with the blanketbeing of the sa-me material and thickness in all duct sizes. These wires when formed into the continuous vhelix of these sizes give excellent radial strength against collapse to the l duct, but it should be noted that if these wires are removed from the mandrels Without remaining secured to the insulation blanket or being secured to .anything else,

the coils of wire would merely collect into a randomly arranged and intertwined series 4of coils rather than forming a coil spring with substantially regular axial spacing between each convolution of wire.

In this sense the helix of our invention may be said to be, except radially of each individual coil, dimentionally unstable. While no of wire to use fora particular size duct., since many variations can be used, itis to be noted that the Wire of any ,y

particular composition and hardness cannot exceed certain sizes` of wire diameter for certain sizes of ducts. A

wire of sutiicient rigidity to form la self-supporting coil Q spring of these sizes and capable of maintaining their spaced convolutions, commonly referred yto as a cornpression coil spring, would be too rigid when incorpoof an operable compression coil spring that can be fabricated. This upper limit in spring diameter when using round spring steel wire is Aroughly 40 times the diameter of the wire, whereas it can be seen from `the above that the diameter of the wire helix of ou-r duct s over l0() for a duct of larger than 3.7 inches inside diameter and `particular formula has been devised for selecting the size even as high as over 300 times the diameter of the spring steel wire for a duct of 16 inside diameter. Stated differently, 'the wire helix of our d-uct is of such a large helix diameter in relation to the wire cross-sectional size. composition and hardness that the helix is inherently dimensiona-lly unstable except in a direction radially of each coil individually. Thus, in effect, the insulation blanket supplies the longitudinal strength and axial stability While the Wire supplies the radial strength against collapse.

Since the wire 72 is exposed to the interior of the duct,

We prefer to use a wire which resists corrosion. We

have found galvanized steel spring wi re and copper wire to'be highly satisfactory although other types of wire, as heretofore defined, may be use-d. Although the Wire 72 is deformed by being wrapped on the mandrels 29 and 30 to form circular convolutions which tend to conform to the size of the mandrels, when the wire is unclamped from the mandrels and the mandrels are collapsed the y lcured by adhesive to the insulation blanket.

4Lthe Wire only embeds itself in the insulation blanket to a y,depth about equal to the diameter of thewire. The wire continually tends to expand slightly outwardly due to Iits own resiliency. The wire -is prevented from excessive circumferential expansion .due to the insulation blanket having a certain yamount of strength to resist circumferential stretching, particularly in' part due to .the fiber 'orientation'p'reviously described, and the wire being sel iFurther, .radial expansion of the entire duct is limited by the sleeve v v`v86and tie cord 85er other means employed to secure vthe end 84 of the blanket. v Ithas also been found that it is unnecessary to use a tie cord LSS-oxj 'other permanent securing means on the blanket ifa sutlciently strong sleeve 86 is used which will resist the radial expansion of the entire duct. When the `tie cord 85 is omitted, it has been found satisfactory to aise a length of non-adhesive cellophane tape which is.

position the. tape may be released andl pulled out from I between the sleeve 86 and the blanket S0. 1

Since the insulation blanket 80 is easily compressed the Aoverlapping of wraps of'insulation blanket donot form excessive bulges in the finished duct as may be seen in 72 is maintained dueto being secured to the insulation blanket in spaced relationship and the insulation blanket 'having suicient longitudinal strength to resist axial elongation of the' entire duct. When the duct is exed around a corner, as shown in FIGURE 5, the outer radius portion `91 of` the duct merely bends whereby any wrinkles in the material of sleeve 86 are straightened out but this portion of the material of the sleeve is not appreciably ystretched lengthwise; whereasthe inner radius portion 92 l `of the duct is compressed so that the adjacent convolutions of wire 72 are brought closer together while the ,insulation blanket merely compresses and the `sleeve 86 assumes afolded condition around the curve. Thus the length of the axis of the duct is actually foreshortened upon bending of the duct. The wires 72 remain secured J- tothe insulation blanket so that if the duct is returned to its original straight ycondition the convolutions of wires will return to their original spaced condition. The cylindrical conliguration of the duct is structurally maintained vonly by the convolutions of wire 72 since the insulation blanket 80 is exible and compressible and the sleeve 86 is also flexible. As the duct is` flexed around a corner as in FIGURE 5,jthe circular cross-section of the duct is substantially maintained by the convolutions of wire 72 and, therefore, .the inside diameter D' of the duct at ythe bend is substantially the same as the'normal diameter 'D of the duct. The relatively smooth interior surface of the duct is not adversely affected byV exing the duct around acorner since theinsulation blanket is merely compressed ratherv than bulging inwardly. This compression rather than bulging is further enhanced by thel "and to comply with some building ordinances and codes.

-The glue or adhesive is also preferably of a type which remains exible after setting so that the duct may be y FIGURE 3. The spacing between convolutions of wire flexed without damaging the bond between the wire andv insulation'blanket. We have found various rubber-base adhesives to be satisfactory, such` as the adhesive vmanufactured and sold under the trademark Hypolonv by the Lurado' Manufacturing Co. of Anaheim, California, and those which may be thinned with methylene chloride or other nondiammable type thinners. .The adhesivev glue, or coating, which is sprayed onvthe insulation. blanket may be of the-same or a similar typewhich will inhibit fiber erosion -of the insulation blanket when air iiows through the duct.

In the modified form of our duct shown in FIGURE 6, the wire 72a is glued and wound onto a collapsible mandrel and one or more wraps of insulation blanket 60a are wrapped onto the wire as previously described. A tie cord 85a may then be vapplied and a sleeve 86a installed as previously described. One or more additional wraps of insulation blanket 80b are then wrapped around the sleeve 86a, a tie cord SSb is applied, and an outer 'tiexible sleeve 86b is installed over the entireassembly. This modified form of duct is adapted to withstand higher internal air pressures than the duct previously described due to the double sleeves 86a and 86b.

In the modified form of our invention shown in FIG- URE 8 the 'wire framework is comprisedof two separate continuous wires 72b and y72e wound onto a collapsible mandrel side-by-side at the same time in a manner similar to our preferred form. For making Ithis modified yform on the aforo-described apparatus, it is preferred that the apparatus be provided with two separate wire feeding assemblies 61 and adhesive applicators 63 to accommodate the two separate wires. The wires are coated with adhesive and an insulation-'blanket Slc is wrapped v around the wires in the manner previously described. A

flexible sleeve 86e. is also installed in the previously described manner. Likewise, more than two separate wires `could be used if so desired.

In the modified form 'of our invention shown in FIG- URES 9, 10 and ll', the semi-cyclindrical mandrels 29 and 30 of the collapsible mandrel assembly 24 are replaced with rectangular mandrels 29d and 30d. The mandrels 29d and 30d have rounded corners 99 to prevent excessive stressing of the wire 72d as the wire is wound onto the mandrels in a manner substantially the same as previously described. The mandrels 29d and 30d are collapsible toward each other the same as mandrels 29 and 30. The wire 72d is glued and wrapped onto the mandrels 29d and 30d, the insulated blanket 80d is wrapped around the glued wire and'mandrels, .and the tie cord d is applied, all in a manner similar to the vmanner previously described. A flexible sleeve A86a' is installed in a manner similar to theinstallation of sleeve 86, except that hoops ofa rectangular Shape are used instead of the circular hoops 87 and S8. This duct will have a rectangular cross-section as shown in FIGURE l0 while the duct is still on the mandrels 29d and 30d, but when removed from the mandrels will tend to assume an irregular rectangular crosssection similar to that shown in FIG- URE 11. This'form of duct is particularly useful in relatively flat restricted spaces since although the duct normally has the coniguration shown in FIGURE 11 the sides may be pressed in to force the duct into the configuration shown in FIGURE 10, thereby maximizing the cross-sectional air-dow area while minimizing the lateral dimensions of the duct.

In some air conditioning and heating system installations it is necessary to t a duct between two previously installed ducts, plenums, or registers to transmit air from one to theother. In FIGURE 7`is shown a main air plenum 93 with a cylindrical conduit 94 tap-o opening which is to be connected to the cylindrical conduit 9S of the register 96. As shown the conduits 94 and 95 may be substantially oiiset from one another. The duct of our invention is inserted over one of the conduits, shown on conduit 95, and an adhesive tape 97 is spiral-wrapped through the layers of blanket.

beyond the end of the insulation blanket 80, as shown inv :maitresse v onto the conduit and onto the outside of the duct, thereby securing -the duct to the conduitv and forming an air-,tight seal. Note that the tape 97 compresses the end of the duct. The other' end of the duct may then be compressed v longitudinally, yas at 98 and inserted over the conduit 91S.

. therefore, preferto provide means for enclosing the ends ofthe duct to prevent this unravelling and these means may be comprised of those shown in FIGURES 12 through 16. After the glued wire 72 has been wrapped onto the. collapsible mandrel 24 (shown in FIGURES 12-16 as solid for simplicity), as heretofore described, a length of flexible material 100, such as vinyl, is Wrapped around the wire and mandrel with a portion of the material 100 extending beyond the last convolution of wire, as Shown in FIGURE 12. The material 100 is secured in this position such as by tape 101.' The insulation blanket 80 is then wrapped on the mandrel and Wire, and securedby any convenient means such as a tie cord, as heretofore described, or by staples 102 driven into and The material 100 extends FIGURE 13. Another length of the flexible material tightly around the end portion of the blanket 80 and secured thereto by any convenient means such as staples A104, as shown in FIGURE 14. The portion of material 100 that extends beyond the wire 72, blardret 80 and material 103 is then pulled back overthe top of material 103 and secured thereto such as by staples 105, as shown in FIGURES 15 and 15A, thus enclosing the end of the 'insulation blanket 80. The sleeve 86 is then pulled over the insulation 4blanket as heretofore described thus completing the duct in the normal manner. It is preferred that a sleeve of excess length -be used so that a portion 106 of the end may bedoubled back, as shown in FIG- URE 16, until used for connecting to another duct.

In FIGURE 17 there is shown a manner for connecting the ends of two ducts in air-tight relation. A rigid or semi-rigid tube 107 is inserted inside one duct a distance of about half the tubes length. The tube is then secured to the duct by any convenient means such as tape 108. The extending end ofthe tube is then inserted-into another duct and if the end of the other duct is provided with a doubled back portion 106 of sleeve 86, then portion 106 is pulled over the exterior of the rst duct. The ducts are joined by securing their sleeves S6 together such as by merely wrapping tape (not shown in FIGURE 17) around the sleeves 86 at the juncture. Thus, an air-tight connection is formed and although the presence of tube 107 interferes with the flexibility and acoustical `insulation characteristics of the duct at this point, this has not been foundv objectionable since the tube 107 is extremely short relative to the overall length of the duct.

Thus, it may be seen that we have provided a flexible ductwhich is relatively inexpensive, easy to install, has good air-flow characteristics,` and is both thermal and v acoustical insulating. The structure of our duct is such that therange of thermal insulating properties which may be obtained is not limited since it is merely necessary to provide more or fewer wraps of insulation blanket or to provide a different type of insulation blanket as requirements dictate. The interior surface of our duct is relatively smooth and consistent in cross-sectional tiow area even though the duct is flexed around thecorner.

Having fully described our invention, it is to be understood that we do not wish to be limited to the details blanket to remain substantially constant along the length 1 herein set forth or to the details illustrated in the drawings, whether such details be as to structure or materials, but our invention is of the full scope of Ithe appended claims.

We claim:

1. In a duct the combination of: a continuous wire forming a helix having spaced convolutions, a tubular more than slight radial compression of the insulation material against the convolutions of the wire helix thereby permitting the thickness of the tubular member to remain substantially constant along the length of the duct.

2. In a duct the combination of: a continuous wire forming .a helix having spaced convolutions, a tubular blanket of porous compressible insulating material encircling said wire helix with substantially the entire inner surface exposed as and forming the inner surface of the duct, said blanket being secured directly to said wire helix l, for maintaining the spacing of the convolutions of wire,

and a flexible substantially nonexpansble sleeve encircling said blanket, said sleeve being of a normal inside diameter relative to the outside diameter of the helix and to the normal inside and outside diameters of the tubular blanket and said sleeve being of a firmness only sufficient to provide no more than slight radial compression of the insulation material against the convolutions of the wire helix thereby permitting the thickness of the of the duct.

3.y The duct of claim 2 wherein said means for main-l I' surface of the duct, and means for maintaining the wire convolutions in spaced relation to each other while the duct is in an unflexed condition, said tubular member having a normal inside diameter substantially equal to the diameter of the wire convolutions and said tubular ,j f

member being retained in encircling relation on said wire helix withinteracting radial forces between said tubular member and wire helix of a magnitude only suicient to provide no more than slight radial compression of the insulation material against the convolutions of the wire helix thereby permitting the thickness of the member to remain substantially constant along the length of the duct.

5. The duct of claim 4 wherein the wire helix per se is self sustaining only radially of each individual coil.

6. The ductl of claim 4 wherein the diameter of such Wire helix in the duct is less than the diameter of said helix in an unrestrained condition for the convolutions of the wire helix to tend to expand slightly in a radial direction.

7. The duct of claim 4 wherein the ratio of the diameter of the wire helix to the diameter of the wire is from about :1 to 300:1.

S. The duct of claim 4 wherein the said means for maintaining the wire convolutions in spaced relation is an adhesive adhering said convolutions directly to the ini sulation material.

9. The duct of claim 4 wherein the insulation material y has a density of about 0.3 to 1.0 pound per cubic foot and is composed of glass fibers disposed angularly to each sleeve encircles said tubular member.

li. H

Y othe'r but oriented generally around the circumference of the duct.

10. The ductof claim 4 wherein the'said wire helix perse is dimensionally unstable in the axial direction of the` helix,.said wire helix has a diameter in the duct less -than the diameter lof said wire helix-in an unrestrained condition thereof for causing said convolutions of the 'Wirehelixto tend to expand slightly in a radial direction and said means for maintaining the wire helix convolutions infspaced relation includes an adhesive adhering 'said vfigw'ire helix directly to said insulation material. v l

11. The -duct of claim 4 wherein said means for main- *taining the wire convolutions invspaced relation comprises means securingsaidmembei to said wire helix.

12. TheV ductof claim-4 wherein said wire helix is 13. The duct of claim 4 wherein a flexible impervious 14. The duct of claim 13 wherein a second sleeve of u ',iexible material 'enclose's the insulation material of at least one end of the duct, said second sleeve having a portion positioned between said wire helix and said insulation material and 'having another portion doubled back over the end of said insulation material, said last-mentioned portionpositioned between said insulation material and said first sleeve, said first sleeve being of a length and unattached to said second sleeve, for extending beyond its end of the duct for cooperating with and connecting to other duct means.

References Cited bythe Examiner V UNITED STATES PATENTS 1,009,465 11/11 ABowers Q 1385-131 1,872,540 8/32 White 13S-109 X 2,011,781 8/35 TabOZZi 138--131 2,050,023 8/36 Slaytel'y 285- -293 2,226,523 12/40 Peck ea 138-149 X 2,312,282 2/43 Peet 1384-137 2,330,966 10/43 Gottwald et a1 138-,149 2,580,872 1/52 Wise 138--131 2,597,806 5/52 Martin 13S-122 2,790,464v 4/ 57 Stephens et al 138-149 X 2,858,854 11/58 Daggett. t 2,861,598 11/58 Carder et al.' 13S-133 2,943,644 7/60 Moseley 138-139 X 2,949,133 8/60 R0thermel et al. 138133 X 2,980,144 4/61 Edwards et al.l 138-131 X LAVERNE D. GEIGER, Primary Examiner. LEWIS J. LENNY, EDWARD v.v BENHAM, Examiners. 

1. IN A DUCT THE COMBINATION OF: A CONTINUOUS WIRE FORMING A HELIX HAVING SPACED CONVOLUTIONS, A TUBULAR MEMBER OF POROUS COMPRESSIBLE INSULATING MATERIAL ENCIRCLING SAID WIRE HELIX WITH SUBSTANTIALLY THE ENTIRE INNER SURFACE EXPOSED AS THE INNER SURFACE OF THE DUCT, MEANS FOR MAINTAINING THE WIRE CONVOLUTION IN SPACED RELATION TO EACH OTHER, AND A SLEEVE ENCIRCLING SAID MEMBER, SAID SLEEVE HAVING A NORMAL INSIDE DIAMETER RELATIVE TO THE OUTSIDE DIAMETER OF THE HELIX AND TO THE NORMAL INSIDE AND OUTER DIAMETERS OF THE TUBULAR MEMBER AND SAID SLEEVE BEING OF A FIRMNESS ONLY SUFFICIENT TO PROVIDE NO MORE THAN SLIGHT RADIAL COMPRESSION OF THE INSULATION MATERIAL AGAINST THE CONVOLUTIONS OF THE WIRE HELIX THEREBY PERMITTING THE THICKNESS OF THE TUBULAR MEMBER TO REMAIN SUBSTANTIALLY CONSTANT ALONG THE LENGTH OF THE DUCT. 